The present invention relates to a mirror surface state detection device which detects the state on a mirror surface and a moisture detection device which detects moisture contained in a target measurement gas condensed on the mirror surface.
Conventionally, as a humidity measuring method, a dew point detection method is known, in which the temperature of a target measurement gas is decreased, and the temperature at which vapor contained in the target measurement gas partially condenses is measured, thereby detecting the dew point. For example, “The Outline of Industrial Measurement Technology 10, Temperature/Moisture Measurement”, Nikkan Kogyo Shimbun, pp. 87–91 (reference 1) describes a mirror surface cooling dew point detector which cools a mirror by using a freezing mixture, refrigerator, or electronic cooler, detects a change in intensity of reflected light on the mirror surface of the cooled mirror, and measures the temperature of the mirror surface at this time, thereby detecting the dew point of moisture in the target measurement gas.
Mirror surface cooling dew point detectors are classified into two types depending on the type of reflected light to be used. One type uses a regular-reflected light detection method using regular-reflected light proposed in Japanese Patent Laid-Open No. 61-75235. The other type uses a scattered light detection method using scattered light proposed in Japanese Patent Laid-Open No. 63-309846.
[Regular-Reflected Light Detection Method]
FIG. 18 shows the main part of a conventional mirror surface cooling dew point detector which employs the regular-reflected light detection method. A mirror surface cooling dew point detector 101 comprises a chamber 1 in which a target measurement gas flows and a thermoelectric cooling element (Peltier element) 2 provided in the chamber 1. A bolt 4 is attached to a cooled surface 2-1 of the thermoelectric cooling element 2 through a copper block 3. A radiating fin 5 is attached to a heated surface 2-2 of the thermoelectric cooling element 2. An upper surface 4-1 of the bolt 4 attached to the copper block 3 is a mirror surface.
A wire-wound resistance thermometer sensor (temperature detection element) 6 is embedded in the side part of the copper block 3 (FIG. 22). A light-emitting element 7 which obliquely irradiates the upper surface (mirror surface) 4-1 of the bolt 4 with light and a light-receiving element 8 which receives the regular-reflected light of light emitted from the light-emitting element 7 to the mirror surface 4-1 are provided at the upper portion of the chamber 1. A heat insulator 40 is provided around the thermoelectric cooling element 2.
In the mirror surface cooling dew point detector 101, the mirror surface 4-1 in the chamber 1 is exposed to the target measurement gas flowing into the chamber 1. If no condensation occurs on the mirror surface 4-1, the light emitted from the light-emitting element 7 is almost wholly regularly reflected and received by the light-receiving element 8. Hence, when no condensation occurs on the mirror surface 4-1, the intensity of reflected light received by the light-receiving element 8 is high.
As the current to the thermoelectric cooling element 2 is increased to lower the temperature of the cooled surface 2-1 of the thermoelectric cooling element 2, vapor contained in the target measurement gas condenses on the mirror surface 4-1. The light emitted from the light-emitting element 7 is partially absorbed or diffused by the molecules of water. The intensity of the reflected light (regular-reflected light) received by the light-receiving element 8 decreases. When the change in regular-reflected light on the mirror surface 4-1 is detected, the change of the state on the mirror surface 4-1, i.e., adhesion of moisture (water droplets) on the mirror surface 4-1 can be recognized. In addition, when the temperature of the mirror surface 4-1 at this time is measured indirectly by the temperature detection element 6, the dew point of moisture in the target measurement gas can be detected.
[Scattered Light Detection Method]
FIG. 19 shows the main part of another conventional mirror surface cooling dew point detector which employs the scattered light detection method. A mirror surface cooling dew point detector 102 has almost the same arrangement as the mirror surface cooling dew point detector 101 using the regular-reflected light detection method except the mount position of the light-receiving element 8. In the mirror surface cooling dew point detector 102, the light-receiving element 8 is provided not at the position to receive the regular-reflected light of light emitted from the light-emitting element 7 to the mirror surface 4-1 but at the position to receive scattered light.
In the mirror surface cooling dew point detector 102, the mirror surface 4-1 is exposed to the target measurement gas flowing into the chamber 1. If no condensation occurs on the mirror surface 4-1, the light emitted from the light-emitting element 7 is almost wholly regularly reflected, and the amount of light received by the light-receiving element 8 is very small. Hence, when no condensation occurs on the mirror surface 4-1, the intensity of reflected light received by the light-receiving element 8 is low.
As the current to the thermoelectric cooling element 2 is increased to lower the temperature of the cooled surface 2-1 of the thermoelectric cooling element 2, vapor contained in the target measurement gas condenses on the mirror surface 4-1. The light emitted from the light-emitting element 7 is partially absorbed or diffused by the molecules of water. The intensity of the diffused light (scattered light) received by the light-receiving element 8 increases. When the change in scattered light on the mirror surface 4-1 is detected, the change of the state on the mirror surface 4-1, i.e., adhesion of moisture (water droplets) on the mirror surface 4-1 can be recognized. In addition, when the temperature of the mirror surface 4-1 at this time is measured indirectly by the temperature detection element 6, the dew point of moisture in the target measurement gas can be detected.
In the above-described dew point detectors, condensation (moisture) on the mirror surface 4-1 is detected. With the same arrangement as described above, frost (moisture) on the mirror surface 4-1 can also be detected.
The arrangement shown in FIG. 20 or 22 can also be employed. More specifically, the thermoelectric cooling element 2 and temperature detection element 6 are omitted. Only a mirror 9 is provided in the chamber 1. An opening portion is provided in the upper surface of the chamber 1. In this case, the detector can be used as a mirror surface state detection device (weather detector) which detects moisture sticking to a mirror surface 9-1 when it begins to rain or snow. In a weather detector 103 or 104, when rain or snow falls into the chamber 1 and sticks to the mirror surface 9-1, it is detected on the basis of the intensity of reflected light received by the light-receiving element 8.
However, according to the above-described conventional mirror surface cooling dew point detector 101 or 102 or weather detector 103 or 104, the light-emitting element 7 and light-receiving element 8 are independently installed at different tilt angles such that they should maintain a predetermined positional relationship. For this reason, the chamber 1 inevitably becomes bulky, and size reduction cannot be promoted. Additionally, since the light-emitting element 7 and light-receiving element 8 are separately arranged at different angles, alignment between the light-emitting element 7 and the light-receiving element 8 in assembly is difficult, resulting in poor workability.
In the mirror surface cooling sensor 101 or 102 shown in FIG. 18 or 19, the lower limit of dew point measurement is determined by how low the temperature of the cooled surface 2-1 of the thermoelectric cooling element 2 can be made. For this reason, in another mirror surface cooling sensor, to further cool the cooled surface 2-1 of the thermoelectric cooling element 2, one end of a heat pipe is attached to the heated surface 2-2 of the thermoelectric cooling element 2. The radiating member 5 is attached to the other end of the heat pipe spaced apart from the thermoelectric cooling element 2. With this structure, heat generated in the heated surface 2-2 moves from one end to the other end of the heat pipe and dissipated through the radiating member 5. In addition, by providing the heat insulating member, the heat from the heated surface 2-2 of the thermoelectric cooling element 2 and the heat pipe is prevented from returning to the chamber 1 and mirror member.
In the above-described mirror surface cooling sensor, the light-emitting element 8 and light-receiving element 9 are fixed in the chamber 1. A lead wire is connected to the thermoelectric cooling element 2 through the heat insulating member integrally fixed to the heat pipe. For this reason, it is difficult to exchange the light-emitting element 8, light-receiving element 9, or thermoelectric cooling element 2 on the site. In addition, position adjustment of the mirror member, light-emitting element 8, or light-receiving element 9 on the site is difficult. For mirror surface cooling sensors of this type, it is demanded to facilitate maintenance such as adjustment and exchange of components in the sensor to cope with the environmental difference of the installation site or the difference of required measurement accuracy.